The present invention relates to a bearing for supporting a high-speed rotation shaft of, for example, a centrifugal compressor, and in particular relates to a squeeze film damper bearing.
In general, a squeeze film damper bearing is a bearing of a type such that fluid film is formed between a fixed surface and the bearing for support of a rotation shaft, thereby supporting the bearing by fluid film pressure. The bearing is particularly characterized by its effect of decreasing any vibration of the shaft being rotated at high speed, and is much useful as a bearing for a turbocompresser, a turbocharger or the like.
A typical example of such squeeze film damper bearing is disclosed in JP-A-58-109718 wherein an oil film is formed by supplying oil into a gap between a fixed support surface and an outer ring presser of a roller bearing. The presser is supported by a number of bolts which extend in parallel with the shaft and enclose the shaft from the fixed side, these bolts serving as spring means. In this way, the bearing is supported by the spring means and by the oil film provided in parallel with the spring means to thereby provide the squeeze film damper bearing.
However, the bearing with the above-mentioned structure is difficult to assemble with higher accuracy and therefore is much expensive. It also requires axially much space and therefore is hardly applicable in a small-sized rotating machine which is limited in space. Japanese Patent Application No. 7-60683 (JP-A-8-261231) was filed by the owner of the present application to overcome this problem.
The bearing disclosed in JP-A-8-261231 comprises a bearing metal for supporting a rotation shaft, a bearing casing for covering the bearing metal, and highly rigid concentricity spring means in the form of arcuate members between the bearing metal and the bearing casing. The bearing metal is stepped to have reduced diameter at its laterally opposite ends. The bearing casing is formed at its inner surface with an annular groove faced to the above-mentioned stepped portions of the bearing casing. The spring means is placed between the groove and the stepped portions and comprises arcuate members, i.e., circumferentially equiangularly divided portions of cylinder. The arcuate member has outer projections in parallel with an axis and equiangularly spaced apart from each other to be at circumferentially opposite ends and at a midway portion. The arcuate member further has inner projections in parallel with the axis and each midway between the adjacent outer projections. The inner and outer projections of the members are contacted with the stepped portions of the bearing metal and support surfaces of the grooved inner bottom of the bearing casing, respectively, so that the bearing metal is supported by the bearing casing via the concentricity spring means to provide a gap between the outer periphery of the bearing metal and the inner surface of the bearing casing. Further, an oiling passage is communicated to the gap so as to generate oil film pressure as required.
Meritorious effects of the above bearing will be explained.
The bearing metal is supported by the support surface of the bearing casing via the projections on the concentricity spring means. As a result, a gap with a predetermined dimension is formed between the outer periphery of the bearing metal and the inner surface of the bearing casing. Oil is supplied into the gap to generate oil film pressure as required. The high rigidity of the spring means will assure the oil film since it prevent the surface of the bearing metal from being directly contacted with the inner surface of the bearing casing even when high vibrating or whirling force is applied on the shaft.
The spring means comprises circumferentially divided arcuate members which are slightly deformable by pressure of the bearing casing to be adapted well to the shape of the gap between the outer periphery of the stepped portion of the bearing metal and the support surface of the bearing casing which covers the bearing metal. As a result, close contact of the bearing metal and bearing casing with the inner and outer projections of the spring means can be maintained even when manufacturing accuracy may be somewhat low, and the bearing can be supported with high accuracy. Further, support of the bearing metal via the spring means can be achieved independently from and in parallel with support of the bearing metal via the oil film, so that an attenuating effect of the oil film can be estimated by calculation.
In the squeeze film damper bearing as described above, the spring means usually used comprises semi-circular members, and two of such spring members, i.e. upper and lower spring members, are used in combination. Each of the spring members has outer projections in parallel with the axis and provided at an apex and circumferentially opposite ends. The spring member further has inner projections in parallel with the axis and provided at 45.degree. to the horizontal. Such spring members are produced by masking portions of a cylindrical body which correspond to the inner and outer projections as required and caving the other portions by etching. Then, the etched portions are formed in concave shape while the masked portions are formed in projected shape. The cylindrical body is, then, cut off along a plane passing through centers of the diametrically opposite outer projections and including the axis to thereby provide the spring members. The height of each of the projections may be in the order of several hundred .mu.m.
As described above, the concentricity spring means used in the squeeze film damper bearing is produced by machining and etching from a thick cylindrical body, which results in higher material and fabricating cost. Moreover, dimensional restriction may make it difficult to vary the spring constant in wide range in accordance with operating conditions.
To solve the above problems in the prior art, it is an object of the present invention to provide a squeeze film damper bearing with concentricity spring means, which can be produced at low cost and in which spring constant can be varied in wide range.